1. Field of the Invention
The present invention relates generally to optical systems. The present invention relates more particularly to micro electromechanical (MEM) devices that may be used in optical systems.
2. Description of the Background Art
Arrays of light-modulating elements have been applied to communications and display systems. The light-modulating elements may comprise, for example, the GLV(trademark) light modulator available from Silicon Light Machines in Sunnyvale, Calif. For example, the arrays may be used as a micro electromechanical system (MEMS) for use in optical networks. In another application, a two-dimensional projection image may also be formed by using one or more linear arrays of light-modulating elements. In such display systems, the linear array modulates an incident light beam to display pixels along a column (or, alternatively, a row) of the two-dimensional (2D) image. A scanning system is used to move the column across the screen such that each light-modulating element is able to generate a row of the 2D image. In this way, the entire 2D image is displayed.
Publications describing GLV(trademark) light modulator devices and their applications include, among others: xe2x80x9cThe Grating Light Valve: Revolutionizing Display Technology,xe2x80x9d by D. M. Bloom, Projection Displays III Symposium, SPIE Proceedings, Volume 3013, San Jose, Calif., February 1997; xe2x80x9cGrating Light Valve Technology: Update and Novel Applications,xe2x80x9d by D. T. Amm and R. W. Corrigan of Silicon Light Machines in Sunnyvale, Calif., a paper presented at the Society for Information Display Symposium, May 19, 1998, Anaheim, Calif.; xe2x80x9cOptical Performance of the Grating Light Valve Technology,xe2x80x9d David T. Amm and Robert W. Corrigan of Silicon Light Machines, a paper presented at Photonics West-Electronics Imaging, 1999; xe2x80x9cCalibration of a Scanned Linear Grating Light Valve Projection System,xe2x80x9d R. W. Corrigan, D. T. Amm, P. A. Alioshin, B. Staker, D. A. LeHoty, K. P. Gross, and B. R. Lang, a paper presented at the Society for Information Display Symposium, May 18, 1999, San Jose, Calif.; xe2x80x9cAn Alternative Architecture for High Performance Display,xe2x80x9d R. W. Corrigan, B. R. Lang, D. A. LeHoty, and P. A. Alioshin of Silicon Light Machines, a paper presented at the 141st SMPTE Technical Conference and Exhibition, Nov. 20, 1999, New York, N.Y.; xe2x80x9cBreakthrough MEMS Component Technology for Optical Networks,xe2x80x9d Robert Corrigan, Randy Cook, and Olivier Favotte, Silicon Light Machinesxe2x80x94Grating Light Valve Technology Brief, 2001; and U.S. Pat. No. 6,215,579, entitled xe2x80x9cMethod and Apparatus for Modulating an Incident Light Beam for Forming a Two-Dimensional Image,xe2x80x9d and assigned at issuance to Silicon Light Machines. Each of the above-mentioned publications is hereby incorporated by reference in its entirety.
One disadvantageous aspect of using such light modulators and other MEMS technology relates to changes in device performance as a function of time. Whether used in a communication or other system, the response function of a light modulator element and other MEM devices has been observed to change over time. Such time-dependent changes can lead to unpredictable behavior and thus may limit the applications for light modulator elements and other MEM devices.
One embodiment of the invention pertains to a method for driving a micro electromechanical (MEM) device. The method includes generating a high-frequency AC drive signal that is substantially higher in frequency than a resonance frequency of a movable feature in the MEM device, and modulating the amplitude of the high-frequency AC drive signal. A DC-like displacement of the movable feature in the MEM device is achieved by driving the movable feature using the amplitude modulated high-frequency AC drive signal.
Another embodiment of the invention relates to an apparatus for driving a movable feature in a micro electromechanical (MEM) device to a nearly static displacement level. The apparatus includes a high-frequency signal generator, an amplitude modulator, and a controller. The signal generator generates an AC drive signal that is substantially higher in frequency than a resonance frequency of the movable feature. The amplitude modulator modulates the high-frequency AC drive signal to the appropriate amplitude prior to application of the drive signal to the movable feature in the MEM device. The appropriate amplitude corresponds to a nearly static displacement level and is determined by the controller.
Another embodiment of the invention pertains to a method for driving a micro electromechanical (MEM) device using a square-wave bipolar drive signal. The drive signal is generated such that the transition time between the polarities of the square wave is shorter than the response time of the movable feature of the MEM device. This results in a nearly static displacement of the movable feature.
These and other features of the present invention will be readily apparent to persons of ordinary skill in the art upon reading the entirety of this disclosure, which includes the accompanying drawings and claims.